Sahih al-Bukhari 6782
صحيح البخاري#6782SahihNarrated Ibn `Abbas:The Prophet (ﷺ) said, "When (a person) an adulterer commits illegal sexual intercourse then he is not a believer at the time he is doing it; and when somebody steals, then he is not a believer at the time he is stealing
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 86:11